Over the last years, the number of portable computers and other mobile nodes which support communication by means of the Internet Protocol (IP) has increased dramatically. Since continuous connectivity to IP based networks such as the Internet is generally desired by users of such mobile nodes, a lot of effort has been put into the issue of how to facilitate for roaming of a mobile IP node during ongoing communication sessions.
In order for a mobile node to be able to send a sequence of messages to a different node in an IP network and to receive a corresponding sequence of response messages, the IP address of the mobile node has to be fixed, at least during the duration of the message exchange. A contradictory requirement is on the other hand put on the IP address by the Routing mechanisms of the IP network, which require the point of attachment of a node to the IP network to be uniquely identified by an assigned IP address. Thus, when a mobile node moves to a new physical location, the Internet Routing mechanisms require the mobile node to change its IP address.
A solution to this seeming contradiction has been provided by the Internet Engineering Task Force (IETF) specification RFC 3344, “IP Mobility Support for IPv4”.
According to RFC 3344, a mobile node is given a long-term IP address in a home network, and when a mobile node is away from its home network, a care-of address is associated with the mobile node. The care-of address reflects the mobile node's current point of attachment. A centrally located node in the home network, referred to as the Home Agent, maintains the home address as well as keeps track of any care-of address of the mobile nodes subscribing to services in the network serviced by the Home Agent. The Home Agent furthermore intercepts traffic and tunnels datagrams to any such mobile nodes that are currently roaming. If a mobile node changes its point of attachment while roaming, it must update the Home Agent in its home network with information on its new care-of-address. Hence, the solution provided by RFC 3344 provides for a Home Agent through which all communication to the mobile node has to be routed when the mobile node away from its home network. Although providing full mobility, the solution has several disadvantages, one being vulnerability, since all traffic to the mobile nodes subscribing to services within a particular network has to go through a single node—the Home Agent.
The problem of how to provide mobility to nodes communicating via the Internet Protocol has been addressed in other publications, such as the IETF draft: draft-levkowetz-netmob-protocol-00, “Network-Based Localised Mobility Management Protocol” dated Feb. 26, 2007. However, the solutions in these publications suffer from the same disadvantage of vulnerability as the solution provided in RFC 3344.
Hence, there is a desire to facilitate for mobility of nodes communicating via the Internet Protocol in a less vulnerable manner.